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Letter: Spotted knapweed invading ditches

Posted on Jul 30, 2011 at 1:00 p.m.

Something has happened while we have been preoccupied with invasive alien plant species in our lakes: a similar invasion on land has been taking place.

Take a look at what is growing in our ditches and roadsides. Some of those purple blossoms are thistle, but many are spotted knapweed. This import from overseas, which has been in the U.S. over a hundred years, is currently increasing its growing range in this area by 175 percent annually, and it is virtually out of control.

Spotted knapweed gets a start in disturbed soil, but moves into normal soil quickly. It produces a chemical in the soil that kills other plants, and soon it is the only plant species left. Animals will not eat it because of its bitter taste, and it will ruin crop lands quickly. For example, it destroys an alfalfa field's value in two ways: it completely displaces the alfalfa but it itself cannot be eaten by farm animals. The third threat is that it cannot hold soil in place, leading to increased erosion.

Spotted knapweed is difficult to control, and since it spreads easily along roadsides, local government agencies must take the lead in fighting it. Biological controls are largely ineffective (and come with their own nasty side effects), so herbicides are the only real answer right now. The county recently sprayed along my county road (Becker County), but they did such a spotty job that most weeds are still growing well. And the township has done nothing to control knapweed on its roadsides. Since this pest will certainly get in your yards and fields, encourage your local officials to act now.